
<!DOCTYPE HTML>
<html lang="zh-hans" >
    <head>
        <meta charset="UTF-8">
        <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
        <title>unsafe.Sizeof, Alignof 和 Offsetof · Go语言圣经</title>
        <meta http-equiv="X-UA-Compatible" content="IE=edge" />
        <meta name="description" content="">
        <meta name="generator" content="GitBook 3.2.3">
        
        
        
    
    <link rel="stylesheet" href="../gitbook/style.css">

    
            
                
                <link rel="stylesheet" href="../gitbook/gitbook-plugin-katex/katex.min.css">
                
            
                
                <link rel="stylesheet" href="../gitbook/gitbook-plugin-highlight/website.css">
                
            
                
                <link rel="stylesheet" href="../gitbook/gitbook-plugin-fontsettings/website.css">
                
            
        

    

    
        
    
        
    
        
    
        
    
        
    
        
    

        
    
    
    <meta name="HandheldFriendly" content="true"/>
    <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="black">
    <link rel="apple-touch-icon-precomposed" sizes="152x152" href="../gitbook/images/apple-touch-icon-precomposed-152.png">
    <link rel="shortcut icon" href="../gitbook/images/favicon.ico" type="image/x-icon">

    
    <link rel="next" href="ch13-02.html" />
    
    
    <link rel="prev" href="ch13.html" />
    

    </head>
    <body>
        
<div class="book">
    <div class="book-summary">
        
            
            
                <nav role="navigation">
                


<ul class="summary">
    
    

    

    
        
        
    
        <li class="chapter " data-level="1.1" data-path="../">
            
                <a href="../">
            
                    
                    前言
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.1.1" data-path="../ch0/ch0-01.html">
            
                <a href="../ch0/ch0-01.html">
            
                    
                    Go语言起源
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.1.2" data-path="../ch0/ch0-02.html">
            
                <a href="../ch0/ch0-02.html">
            
                    
                    Go语言项目
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.1.3" data-path="../ch0/ch0-03.html">
            
                <a href="../ch0/ch0-03.html">
            
                    
                    本书的组织
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.1.4" data-path="../ch0/ch0-04.html">
            
                <a href="../ch0/ch0-04.html">
            
                    
                    更多的信息
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.1.5" data-path="../ch0/ch0-05.html">
            
                <a href="../ch0/ch0-05.html">
            
                    
                    致谢
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.2" data-path="../ch1/ch1.html">
            
                <a href="../ch1/ch1.html">
            
                    
                    入门
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.2.1" data-path="../ch1/ch1-01.html">
            
                <a href="../ch1/ch1-01.html">
            
                    
                    Hello, World
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.2.2" data-path="../ch1/ch1-02.html">
            
                <a href="../ch1/ch1-02.html">
            
                    
                    命令行参数
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.2.3" data-path="../ch1/ch1-03.html">
            
                <a href="../ch1/ch1-03.html">
            
                    
                    查找重复的行
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.2.4" data-path="../ch1/ch1-04.html">
            
                <a href="../ch1/ch1-04.html">
            
                    
                    GIF动画
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.2.5" data-path="../ch1/ch1-05.html">
            
                <a href="../ch1/ch1-05.html">
            
                    
                    获取URL
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.2.6" data-path="../ch1/ch1-06.html">
            
                <a href="../ch1/ch1-06.html">
            
                    
                    并发获取多个URL
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.2.7" data-path="../ch1/ch1-07.html">
            
                <a href="../ch1/ch1-07.html">
            
                    
                    Web服务
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.2.8" data-path="../ch1/ch1-08.html">
            
                <a href="../ch1/ch1-08.html">
            
                    
                    本章要点
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.3" data-path="../ch2/ch2.html">
            
                <a href="../ch2/ch2.html">
            
                    
                    程序结构
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.3.1" data-path="../ch2/ch2-01.html">
            
                <a href="../ch2/ch2-01.html">
            
                    
                    命名
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.3.2" data-path="../ch2/ch2-02.html">
            
                <a href="../ch2/ch2-02.html">
            
                    
                    声明
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.3.3" data-path="../ch2/ch2-03.html">
            
                <a href="../ch2/ch2-03.html">
            
                    
                    变量
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.3.4" data-path="../ch2/ch2-04.html">
            
                <a href="../ch2/ch2-04.html">
            
                    
                    赋值
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.3.5" data-path="../ch2/ch2-05.html">
            
                <a href="../ch2/ch2-05.html">
            
                    
                    类型
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.3.6" data-path="../ch2/ch2-06.html">
            
                <a href="../ch2/ch2-06.html">
            
                    
                    包和文件
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.3.7" data-path="../ch2/ch2-07.html">
            
                <a href="../ch2/ch2-07.html">
            
                    
                    作用域
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.4" data-path="../ch3/ch3.html">
            
                <a href="../ch3/ch3.html">
            
                    
                    基础数据类型
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.4.1" data-path="../ch3/ch3-01.html">
            
                <a href="../ch3/ch3-01.html">
            
                    
                    整型
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.4.2" data-path="../ch3/ch3-02.html">
            
                <a href="../ch3/ch3-02.html">
            
                    
                    浮点数
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.4.3" data-path="../ch3/ch3-03.html">
            
                <a href="../ch3/ch3-03.html">
            
                    
                    复数
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.4.4" data-path="../ch3/ch3-04.html">
            
                <a href="../ch3/ch3-04.html">
            
                    
                    布尔型
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.4.5" data-path="../ch3/ch3-05.html">
            
                <a href="../ch3/ch3-05.html">
            
                    
                    字符串
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.4.6" data-path="../ch3/ch3-06.html">
            
                <a href="../ch3/ch3-06.html">
            
                    
                    常量
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.5" data-path="../ch4/ch4.html">
            
                <a href="../ch4/ch4.html">
            
                    
                    复合数据类型
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.5.1" data-path="../ch4/ch4-01.html">
            
                <a href="../ch4/ch4-01.html">
            
                    
                    数组
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.5.2" data-path="../ch4/ch4-02.html">
            
                <a href="../ch4/ch4-02.html">
            
                    
                    Slice
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.5.3" data-path="../ch4/ch4-03.html">
            
                <a href="../ch4/ch4-03.html">
            
                    
                    Map
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.5.4" data-path="../ch4/ch4-04.html">
            
                <a href="../ch4/ch4-04.html">
            
                    
                    结构体
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.5.5" data-path="../ch4/ch4-05.html">
            
                <a href="../ch4/ch4-05.html">
            
                    
                    JSON
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.5.6" data-path="../ch4/ch4-06.html">
            
                <a href="../ch4/ch4-06.html">
            
                    
                    文本和HTML模板
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.6" data-path="../ch5/ch5.html">
            
                <a href="../ch5/ch5.html">
            
                    
                    函数
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.6.1" data-path="../ch5/ch5-01.html">
            
                <a href="../ch5/ch5-01.html">
            
                    
                    函数声明
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.2" data-path="../ch5/ch5-02.html">
            
                <a href="../ch5/ch5-02.html">
            
                    
                    递归
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.3" data-path="../ch5/ch5-03.html">
            
                <a href="../ch5/ch5-03.html">
            
                    
                    多返回值
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.4" data-path="../ch5/ch5-04.html">
            
                <a href="../ch5/ch5-04.html">
            
                    
                    错误
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.5" data-path="../ch5/ch5-05.html">
            
                <a href="../ch5/ch5-05.html">
            
                    
                    函数值
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.6" data-path="../ch5/ch5-06.html">
            
                <a href="../ch5/ch5-06.html">
            
                    
                    匿名函数
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.7" data-path="../ch5/ch5-07.html">
            
                <a href="../ch5/ch5-07.html">
            
                    
                    可变参数
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.8" data-path="../ch5/ch5-08.html">
            
                <a href="../ch5/ch5-08.html">
            
                    
                    Deferred函数
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.9" data-path="../ch5/ch5-09.html">
            
                <a href="../ch5/ch5-09.html">
            
                    
                    Panic异常
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.6.10" data-path="../ch5/ch5-10.html">
            
                <a href="../ch5/ch5-10.html">
            
                    
                    Recover捕获异常
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.7" data-path="../ch6/ch6.html">
            
                <a href="../ch6/ch6.html">
            
                    
                    方法
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.7.1" data-path="../ch6/ch6-01.html">
            
                <a href="../ch6/ch6-01.html">
            
                    
                    方法声明
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.7.2" data-path="../ch6/ch6-02.html">
            
                <a href="../ch6/ch6-02.html">
            
                    
                    基于指针对象的方法
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.7.3" data-path="../ch6/ch6-03.html">
            
                <a href="../ch6/ch6-03.html">
            
                    
                    通过嵌入结构体来扩展类型
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.7.4" data-path="../ch6/ch6-04.html">
            
                <a href="../ch6/ch6-04.html">
            
                    
                    方法值和方法表达式
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.7.5" data-path="../ch6/ch6-05.html">
            
                <a href="../ch6/ch6-05.html">
            
                    
                    示例: Bit数组
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.7.6" data-path="../ch6/ch6-06.html">
            
                <a href="../ch6/ch6-06.html">
            
                    
                    封装
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.8" data-path="../ch7/ch7.html">
            
                <a href="../ch7/ch7.html">
            
                    
                    接口
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.8.1" data-path="../ch7/ch7-01.html">
            
                <a href="../ch7/ch7-01.html">
            
                    
                    接口是合约
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.2" data-path="../ch7/ch7-02.html">
            
                <a href="../ch7/ch7-02.html">
            
                    
                    接口类型
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.3" data-path="../ch7/ch7-03.html">
            
                <a href="../ch7/ch7-03.html">
            
                    
                    实现接口的条件
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.4" data-path="../ch7/ch7-04.html">
            
                <a href="../ch7/ch7-04.html">
            
                    
                    flag.Value接口
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.5" data-path="../ch7/ch7-05.html">
            
                <a href="../ch7/ch7-05.html">
            
                    
                    接口值
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.6" data-path="../ch7/ch7-06.html">
            
                <a href="../ch7/ch7-06.html">
            
                    
                    sort.Interface接口
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.7" data-path="../ch7/ch7-07.html">
            
                <a href="../ch7/ch7-07.html">
            
                    
                    http.Handler接口
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.8" data-path="../ch7/ch7-08.html">
            
                <a href="../ch7/ch7-08.html">
            
                    
                    error接口
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.9" data-path="../ch7/ch7-09.html">
            
                <a href="../ch7/ch7-09.html">
            
                    
                    示例: 表达式求值
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.10" data-path="../ch7/ch7-10.html">
            
                <a href="../ch7/ch7-10.html">
            
                    
                    类型断言
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.11" data-path="../ch7/ch7-11.html">
            
                <a href="../ch7/ch7-11.html">
            
                    
                    基于类型断言识别错误类型
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.12" data-path="../ch7/ch7-12.html">
            
                <a href="../ch7/ch7-12.html">
            
                    
                    通过类型断言查询接口
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.13" data-path="../ch7/ch7-13.html">
            
                <a href="../ch7/ch7-13.html">
            
                    
                    类型分支
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.14" data-path="../ch7/ch7-14.html">
            
                <a href="../ch7/ch7-14.html">
            
                    
                    示例: 基于标记的XML解码
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.8.15" data-path="../ch7/ch7-15.html">
            
                <a href="../ch7/ch7-15.html">
            
                    
                    补充几点
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.9" data-path="../ch8/ch8.html">
            
                <a href="../ch8/ch8.html">
            
                    
                    Goroutines和Channels
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.9.1" data-path="../ch8/ch8-01.html">
            
                <a href="../ch8/ch8-01.html">
            
                    
                    Goroutines
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.2" data-path="../ch8/ch8-02.html">
            
                <a href="../ch8/ch8-02.html">
            
                    
                    示例: 并发的Clock服务
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.3" data-path="../ch8/ch8-03.html">
            
                <a href="../ch8/ch8-03.html">
            
                    
                    示例: 并发的Echo服务
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.4" data-path="../ch8/ch8-04.html">
            
                <a href="../ch8/ch8-04.html">
            
                    
                    Channels
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.5" data-path="../ch8/ch8-05.html">
            
                <a href="../ch8/ch8-05.html">
            
                    
                    并发的循环
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.6" data-path="../ch8/ch8-06.html">
            
                <a href="../ch8/ch8-06.html">
            
                    
                    示例: 并发的Web爬虫
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.7" data-path="../ch8/ch8-07.html">
            
                <a href="../ch8/ch8-07.html">
            
                    
                    基于select的多路复用
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.8" data-path="../ch8/ch8-08.html">
            
                <a href="../ch8/ch8-08.html">
            
                    
                    示例: 并发的目录遍历
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.9" data-path="../ch8/ch8-09.html">
            
                <a href="../ch8/ch8-09.html">
            
                    
                    并发的退出
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.9.10" data-path="../ch8/ch8-10.html">
            
                <a href="../ch8/ch8-10.html">
            
                    
                    示例: 聊天服务
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.10" data-path="../ch9/ch9.html">
            
                <a href="../ch9/ch9.html">
            
                    
                    基于共享变量的并发
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.10.1" data-path="../ch9/ch9-01.html">
            
                <a href="../ch9/ch9-01.html">
            
                    
                    竞争条件
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.2" data-path="../ch9/ch9-02.html">
            
                <a href="../ch9/ch9-02.html">
            
                    
                    sync.Mutex互斥锁
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.3" data-path="../ch9/ch9-03.html">
            
                <a href="../ch9/ch9-03.html">
            
                    
                    sync.RWMutex读写锁
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.4" data-path="../ch9/ch9-04.html">
            
                <a href="../ch9/ch9-04.html">
            
                    
                    内存同步
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.5" data-path="../ch9/ch9-05.html">
            
                <a href="../ch9/ch9-05.html">
            
                    
                    sync.Once惰性初始化
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.6" data-path="../ch9/ch9-06.html">
            
                <a href="../ch9/ch9-06.html">
            
                    
                    竞争条件检测
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.7" data-path="../ch9/ch9-07.html">
            
                <a href="../ch9/ch9-07.html">
            
                    
                    示例: 并发的非阻塞缓存
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.8" data-path="../ch9/ch9-08.html">
            
                <a href="../ch9/ch9-08.html">
            
                    
                    Goroutines和线程
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.11" data-path="../ch10/ch10.html">
            
                <a href="../ch10/ch10.html">
            
                    
                    包和工具
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.11.1" data-path="../ch10/ch10-01.html">
            
                <a href="../ch10/ch10-01.html">
            
                    
                    包简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.2" data-path="../ch10/ch10-02.html">
            
                <a href="../ch10/ch10-02.html">
            
                    
                    导入路径
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.3" data-path="../ch10/ch10-03.html">
            
                <a href="../ch10/ch10-03.html">
            
                    
                    包声明
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.4" data-path="../ch10/ch10-04.html">
            
                <a href="../ch10/ch10-04.html">
            
                    
                    导入声明
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.5" data-path="../ch10/ch10-05.html">
            
                <a href="../ch10/ch10-05.html">
            
                    
                    包的匿名导入
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.6" data-path="../ch10/ch10-06.html">
            
                <a href="../ch10/ch10-06.html">
            
                    
                    包和命名
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.7" data-path="../ch10/ch10-07.html">
            
                <a href="../ch10/ch10-07.html">
            
                    
                    工具
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.12" data-path="../ch11/ch11.html">
            
                <a href="../ch11/ch11.html">
            
                    
                    测试
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.12.1" data-path="../ch11/ch11-01.html">
            
                <a href="../ch11/ch11-01.html">
            
                    
                    go test
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.2" data-path="../ch11/ch11-02.html">
            
                <a href="../ch11/ch11-02.html">
            
                    
                    测试函数
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.3" data-path="../ch11/ch11-03.html">
            
                <a href="../ch11/ch11-03.html">
            
                    
                    测试覆盖率
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.4" data-path="../ch11/ch11-04.html">
            
                <a href="../ch11/ch11-04.html">
            
                    
                    基准测试
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.5" data-path="../ch11/ch11-05.html">
            
                <a href="../ch11/ch11-05.html">
            
                    
                    剖析
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.6" data-path="../ch11/ch11-06.html">
            
                <a href="../ch11/ch11-06.html">
            
                    
                    示例函数
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.13" data-path="../ch12/ch12.html">
            
                <a href="../ch12/ch12.html">
            
                    
                    反射
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.13.1" data-path="../ch12/ch12-01.html">
            
                <a href="../ch12/ch12-01.html">
            
                    
                    为何需要反射?
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.2" data-path="../ch12/ch12-02.html">
            
                <a href="../ch12/ch12-02.html">
            
                    
                    reflect.Type和reflect.Value
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.3" data-path="../ch12/ch12-03.html">
            
                <a href="../ch12/ch12-03.html">
            
                    
                    Display递归打印
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.4" data-path="../ch12/ch12-04.html">
            
                <a href="../ch12/ch12-04.html">
            
                    
                    示例: 编码S表达式
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.5" data-path="../ch12/ch12-05.html">
            
                <a href="../ch12/ch12-05.html">
            
                    
                    通过reflect.Value修改值
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.6" data-path="../ch12/ch12-06.html">
            
                <a href="../ch12/ch12-06.html">
            
                    
                    示例: 解码S表达式
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.7" data-path="../ch12/ch12-07.html">
            
                <a href="../ch12/ch12-07.html">
            
                    
                    获取结构体字段标签
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.8" data-path="../ch12/ch12-08.html">
            
                <a href="../ch12/ch12-08.html">
            
                    
                    显示一个类型的方法集
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.9" data-path="../ch12/ch12-09.html">
            
                <a href="../ch12/ch12-09.html">
            
                    
                    几点忠告
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.14" data-path="ch13.html">
            
                <a href="ch13.html">
            
                    
                    底层编程
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter active" data-level="1.14.1" data-path="ch13-01.html">
            
                <a href="ch13-01.html">
            
                    
                    unsafe.Sizeof, Alignof 和 Offsetof
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.2" data-path="ch13-02.html">
            
                <a href="ch13-02.html">
            
                    
                    unsafe.Pointer
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.3" data-path="ch13-03.html">
            
                <a href="ch13-03.html">
            
                    
                    示例: 深度相等判断
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.4" data-path="ch13-04.html">
            
                <a href="ch13-04.html">
            
                    
                    通过cgo调用C代码
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.5" data-path="ch13-05.html">
            
                <a href="ch13-05.html">
            
                    
                    几点忠告
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.15" data-path="../appendix/appendix.html">
            
                <a href="../appendix/appendix.html">
            
                    
                    附录
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.15.1" data-path="../appendix/appendix-a-errata.html">
            
                <a href="../appendix/appendix-a-errata.html">
            
                    
                    附录A：原文勘误
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.15.2" data-path="../appendix/appendix-b-author.html">
            
                <a href="../appendix/appendix-b-author.html">
            
                    
                    附录B：作者译者
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.15.3" data-path="../appendix/appendix-c-cpoyright.html">
            
                <a href="../appendix/appendix-c-cpoyright.html">
            
                    
                    附录C：译文授权
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.15.4" data-path="../appendix/appendix-d-translations.html">
            
                <a href="../appendix/appendix-d-translations.html">
            
                    
                    附录D：其它语言
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    

    

    <li class="divider"></li>

    <li>
        <a href="https://www.gitbook.com" target="blank" class="gitbook-link">
            本书使用 GitBook 发布
        </a>
    </li>
</ul>


                </nav>
            
        
    </div>

    <div class="book-body">
        
            <div class="body-inner">
                
                    

<div class="book-header" role="navigation">
    

    <!-- Title -->
    <h1>
        <i class="fa fa-circle-o-notch fa-spin"></i>
        <a href=".." >unsafe.Sizeof, Alignof 和 Offsetof</a>
    </h1>
</div>




                    <div class="page-wrapper" tabindex="-1" role="main">
                        <div class="page-inner">
                            
                                <section class="normal markdown-section">
                                
                                <h2 id="131-unsafesizeof-alignof-&#x548C;-offsetof">13.1. unsafe.Sizeof, Alignof &#x548C; Offsetof</h2>
<p>unsafe.Sizeof&#x51FD;&#x6570;&#x8FD4;&#x56DE;&#x64CD;&#x4F5C;&#x6570;&#x5728;&#x5185;&#x5B58;&#x4E2D;&#x7684;&#x5B57;&#x8282;&#x5927;&#x5C0F;&#xFF0C;&#x53C2;&#x6570;&#x53EF;&#x4EE5;&#x662F;&#x4EFB;&#x610F;&#x7C7B;&#x578B;&#x7684;&#x8868;&#x8FBE;&#x5F0F;&#xFF0C;&#x4F46;&#x662F;&#x5B83;&#x5E76;&#x4E0D;&#x4F1A;&#x5BF9;&#x8868;&#x8FBE;&#x5F0F;&#x8FDB;&#x884C;&#x6C42;&#x503C;&#x3002;&#x4E00;&#x4E2A;Sizeof&#x51FD;&#x6570;&#x8C03;&#x7528;&#x662F;&#x4E00;&#x4E2A;&#x5BF9;&#x5E94;uintptr&#x7C7B;&#x578B;&#x7684;&#x5E38;&#x91CF;&#x8868;&#x8FBE;&#x5F0F;&#xFF0C;&#x56E0;&#x6B64;&#x8FD4;&#x56DE;&#x7684;&#x7ED3;&#x679C;&#x53EF;&#x4EE5;&#x7528;&#x4F5C;&#x6570;&#x7EC4;&#x7C7B;&#x578B;&#x7684;&#x957F;&#x5EA6;&#x5927;&#x5C0F;&#xFF0C;&#x6216;&#x8005;&#x7528;&#x4F5C;&#x8BA1;&#x7B97;&#x5176;&#x4ED6;&#x7684;&#x5E38;&#x91CF;&#x3002;</p>
<pre><code class="lang-Go"><span class="hljs-keyword">import</span> <span class="hljs-string">&quot;unsafe&quot;</span>
fmt.Println(unsafe.Sizeof(<span class="hljs-keyword">float64</span>(<span class="hljs-number">0</span>))) <span class="hljs-comment">// &quot;8&quot;</span>
</code></pre>
<p>Sizeof&#x51FD;&#x6570;&#x8FD4;&#x56DE;&#x7684;&#x5927;&#x5C0F;&#x53EA;&#x5305;&#x62EC;&#x6570;&#x636E;&#x7ED3;&#x6784;&#x4E2D;&#x56FA;&#x5B9A;&#x7684;&#x90E8;&#x5206;&#xFF0C;&#x4F8B;&#x5982;&#x5B57;&#x7B26;&#x4E32;&#x5BF9;&#x5E94;&#x7ED3;&#x6784;&#x4F53;&#x4E2D;&#x7684;&#x6307;&#x9488;&#x548C;&#x5B57;&#x7B26;&#x4E32;&#x957F;&#x5EA6;&#x90E8;&#x5206;&#xFF0C;&#x4F46;&#x662F;&#x5E76;&#x4E0D;&#x5305;&#x542B;&#x6307;&#x9488;&#x6307;&#x5411;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x5185;&#x5BB9;&#x3002;Go&#x8BED;&#x8A00;&#x4E2D;&#x975E;&#x805A;&#x5408;&#x7C7B;&#x578B;&#x901A;&#x5E38;&#x6709;&#x4E00;&#x4E2A;&#x56FA;&#x5B9A;&#x7684;&#x5927;&#x5C0F;&#xFF0C;&#x5C3D;&#x7BA1;&#x5728;&#x4E0D;&#x540C;&#x5DE5;&#x5177;&#x94FE;&#x4E0B;&#x751F;&#x6210;&#x7684;&#x5B9E;&#x9645;&#x5927;&#x5C0F;&#x53EF;&#x80FD;&#x4F1A;&#x6709;&#x6240;&#x4E0D;&#x540C;&#x3002;&#x8003;&#x8651;&#x5230;&#x53EF;&#x79FB;&#x690D;&#x6027;&#xFF0C;&#x5F15;&#x7528;&#x7C7B;&#x578B;&#x6216;&#x5305;&#x542B;&#x5F15;&#x7528;&#x7C7B;&#x578B;&#x7684;&#x5927;&#x5C0F;&#x5728;32&#x4F4D;&#x5E73;&#x53F0;&#x4E0A;&#x662F;4&#x4E2A;&#x5B57;&#x8282;&#xFF0C;&#x5728;64&#x4F4D;&#x5E73;&#x53F0;&#x4E0A;&#x662F;8&#x4E2A;&#x5B57;&#x8282;&#x3002;</p>
<p>&#x8BA1;&#x7B97;&#x673A;&#x5728;&#x52A0;&#x8F7D;&#x548C;&#x4FDD;&#x5B58;&#x6570;&#x636E;&#x65F6;&#xFF0C;&#x5982;&#x679C;&#x5185;&#x5B58;&#x5730;&#x5740;&#x5408;&#x7406;&#x5730;&#x5BF9;&#x9F50;&#x7684;&#x5C06;&#x4F1A;&#x66F4;&#x6709;&#x6548;&#x7387;&#x3002;&#x4F8B;&#x5982;2&#x5B57;&#x8282;&#x5927;&#x5C0F;&#x7684;int16&#x7C7B;&#x578B;&#x7684;&#x53D8;&#x91CF;&#x5730;&#x5740;&#x5E94;&#x8BE5;&#x662F;&#x5076;&#x6570;&#xFF0C;&#x4E00;&#x4E2A;4&#x5B57;&#x8282;&#x5927;&#x5C0F;&#x7684;rune&#x7C7B;&#x578B;&#x53D8;&#x91CF;&#x7684;&#x5730;&#x5740;&#x5E94;&#x8BE5;&#x662F;4&#x7684;&#x500D;&#x6570;&#xFF0C;&#x4E00;&#x4E2A;8&#x5B57;&#x8282;&#x5927;&#x5C0F;&#x7684;float64&#x3001;uint64&#x6216;64-bit&#x6307;&#x9488;&#x7C7B;&#x578B;&#x53D8;&#x91CF;&#x7684;&#x5730;&#x5740;&#x5E94;&#x8BE5;&#x662F;8&#x5B57;&#x8282;&#x5BF9;&#x9F50;&#x7684;&#x3002;&#x4F46;&#x662F;&#x5BF9;&#x4E8E;&#x518D;&#x5927;&#x7684;&#x5730;&#x5740;&#x5BF9;&#x9F50;&#x500D;&#x6570;&#x5219;&#x662F;&#x4E0D;&#x9700;&#x8981;&#x7684;&#xFF0C;&#x5373;&#x4F7F;&#x662F;complex128&#x7B49;&#x8F83;&#x5927;&#x7684;&#x6570;&#x636E;&#x7C7B;&#x578B;&#x6700;&#x591A;&#x4E5F;&#x53EA;&#x662F;8&#x5B57;&#x8282;&#x5BF9;&#x9F50;&#x3002;</p>
<p>&#x7531;&#x4E8E;&#x5730;&#x5740;&#x5BF9;&#x9F50;&#x8FD9;&#x4E2A;&#x56E0;&#x7D20;&#xFF0C;&#x4E00;&#x4E2A;&#x805A;&#x5408;&#x7C7B;&#x578B;&#xFF08;&#x7ED3;&#x6784;&#x4F53;&#x6216;&#x6570;&#x7EC4;&#xFF09;&#x7684;&#x5927;&#x5C0F;&#x81F3;&#x5C11;&#x662F;&#x6240;&#x6709;&#x5B57;&#x6BB5;&#x6216;&#x5143;&#x7D20;&#x5927;&#x5C0F;&#x7684;&#x603B;&#x548C;&#xFF0C;&#x6216;&#x8005;&#x66F4;&#x5927;&#x56E0;&#x4E3A;&#x53EF;&#x80FD;&#x5B58;&#x5728;&#x5185;&#x5B58;&#x7A7A;&#x6D1E;&#x3002;&#x5185;&#x5B58;&#x7A7A;&#x6D1E;&#x662F;&#x7F16;&#x8BD1;&#x5668;&#x81EA;&#x52A8;&#x6DFB;&#x52A0;&#x7684;&#x6CA1;&#x6709;&#x88AB;&#x4F7F;&#x7528;&#x7684;&#x5185;&#x5B58;&#x7A7A;&#x95F4;&#xFF0C;&#x7528;&#x4E8E;&#x4FDD;&#x8BC1;&#x540E;&#x9762;&#x6BCF;&#x4E2A;&#x5B57;&#x6BB5;&#x6216;&#x5143;&#x7D20;&#x7684;&#x5730;&#x5740;&#x76F8;&#x5BF9;&#x4E8E;&#x7ED3;&#x6784;&#x6216;&#x6570;&#x7EC4;&#x7684;&#x5F00;&#x59CB;&#x5730;&#x5740;&#x80FD;&#x591F;&#x5408;&#x7406;&#x5730;&#x5BF9;&#x9F50;&#xFF08;&#x8BD1;&#x6CE8;&#xFF1A;&#x5185;&#x5B58;&#x7A7A;&#x6D1E;&#x53EF;&#x80FD;&#x4F1A;&#x5B58;&#x5728;&#x4E00;&#x4E9B;&#x968F;&#x673A;&#x6570;&#x636E;&#xFF0C;&#x53EF;&#x80FD;&#x4F1A;&#x5BF9;&#x7528;unsafe&#x5305;&#x76F4;&#x63A5;&#x64CD;&#x4F5C;&#x5185;&#x5B58;&#x7684;&#x5904;&#x7406;&#x4EA7;&#x751F;&#x5F71;&#x54CD;&#xFF09;&#x3002;</p>
<table>
<thead>
<tr>
<th>&#x7C7B;&#x578B;</th>
<th>&#x5927;&#x5C0F;</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>bool</code></td>
<td>1&#x4E2A;&#x5B57;&#x8282;</td>
</tr>
<tr>
<td><code>intN, uintN, floatN, complexN</code></td>
<td>N/8&#x4E2A;&#x5B57;&#x8282;&#xFF08;&#x4F8B;&#x5982;float64&#x662F;8&#x4E2A;&#x5B57;&#x8282;&#xFF09;</td>
</tr>
<tr>
<td><code>int, uint, uintptr</code></td>
<td>1&#x4E2A;&#x673A;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td><code>*T</code></td>
<td>1&#x4E2A;&#x673A;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td><code>string</code></td>
<td>2&#x4E2A;&#x673A;&#x5668;&#x5B57;&#xFF08;data&#x3001;len&#xFF09;</td>
</tr>
<tr>
<td><code>[]T</code></td>
<td>3&#x4E2A;&#x673A;&#x5668;&#x5B57;&#xFF08;data&#x3001;len&#x3001;cap&#xFF09;</td>
</tr>
<tr>
<td><code>map</code></td>
<td>1&#x4E2A;&#x673A;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td><code>func</code></td>
<td>1&#x4E2A;&#x673A;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td><code>chan</code></td>
<td>1&#x4E2A;&#x673A;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td><code>interface</code></td>
<td>2&#x4E2A;&#x673A;&#x5668;&#x5B57;&#xFF08;type&#x3001;value&#xFF09;</td>
</tr>
</tbody>
</table>
<p>Go&#x8BED;&#x8A00;&#x7684;&#x89C4;&#x8303;&#x5E76;&#x6CA1;&#x6709;&#x8981;&#x6C42;&#x4E00;&#x4E2A;&#x5B57;&#x6BB5;&#x7684;&#x58F0;&#x660E;&#x987A;&#x5E8F;&#x548C;&#x5185;&#x5B58;&#x4E2D;&#x7684;&#x987A;&#x5E8F;&#x662F;&#x4E00;&#x81F4;&#x7684;&#xFF0C;&#x6240;&#x4EE5;&#x7406;&#x8BBA;&#x4E0A;&#x4E00;&#x4E2A;&#x7F16;&#x8BD1;&#x5668;&#x53EF;&#x4EE5;&#x968F;&#x610F;&#x5730;&#x91CD;&#x65B0;&#x6392;&#x5217;&#x6BCF;&#x4E2A;&#x5B57;&#x6BB5;&#x7684;&#x5185;&#x5B58;&#x4F4D;&#x7F6E;&#xFF0C;&#x867D;&#x7136;&#x5728;&#x5199;&#x4F5C;&#x672C;&#x4E66;&#x7684;&#x65F6;&#x5019;&#x7F16;&#x8BD1;&#x5668;&#x8FD8;&#x6CA1;&#x6709;&#x8FD9;&#x4E48;&#x505A;&#x3002;&#x4E0B;&#x9762;&#x7684;&#x4E09;&#x4E2A;&#x7ED3;&#x6784;&#x4F53;&#x867D;&#x7136;&#x6709;&#x7740;&#x76F8;&#x540C;&#x7684;&#x5B57;&#x6BB5;&#xFF0C;&#x4F46;&#x662F;&#x7B2C;&#x4E00;&#x79CD;&#x5199;&#x6CD5;&#x6BD4;&#x53E6;&#x5916;&#x7684;&#x4E24;&#x4E2A;&#x9700;&#x8981;&#x591A;50%&#x7684;&#x5185;&#x5B58;&#x3002;</p>
<pre><code class="lang-Go">                               <span class="hljs-comment">// 64-bit  32-bit</span>
<span class="hljs-keyword">struct</span>{ <span class="hljs-keyword">bool</span>; <span class="hljs-keyword">float64</span>; <span class="hljs-keyword">int16</span> } <span class="hljs-comment">// 3 words 4words</span>
<span class="hljs-keyword">struct</span>{ <span class="hljs-keyword">float64</span>; <span class="hljs-keyword">int16</span>; <span class="hljs-keyword">bool</span> } <span class="hljs-comment">// 2 words 3words</span>
<span class="hljs-keyword">struct</span>{ <span class="hljs-keyword">bool</span>; <span class="hljs-keyword">int16</span>; <span class="hljs-keyword">float64</span> } <span class="hljs-comment">// 2 words 3words</span>
</code></pre>
<p>&#x5173;&#x4E8E;&#x5185;&#x5B58;&#x5730;&#x5740;&#x5BF9;&#x9F50;&#x7B97;&#x6CD5;&#x7684;&#x7EC6;&#x8282;&#x8D85;&#x51FA;&#x4E86;&#x672C;&#x4E66;&#x7684;&#x8303;&#x56F4;&#xFF0C;&#x4E5F;&#x4E0D;&#x662F;&#x6BCF;&#x4E00;&#x4E2A;&#x7ED3;&#x6784;&#x4F53;&#x90FD;&#x9700;&#x8981;&#x62C5;&#x5FC3;&#x8FD9;&#x4E2A;&#x95EE;&#x9898;&#xFF0C;&#x4E0D;&#x8FC7;&#x6709;&#x6548;&#x7684;&#x5305;&#x88C5;&#x53EF;&#x4EE5;&#x4F7F;&#x6570;&#x636E;&#x7ED3;&#x6784;&#x66F4;&#x52A0;&#x7D27;&#x51D1;&#xFF08;&#x8BD1;&#x6CE8;&#xFF1A;&#x672A;&#x6765;&#x7684;Go&#x8BED;&#x8A00;&#x7F16;&#x8BD1;&#x5668;&#x5E94;&#x8BE5;&#x4F1A;&#x9ED8;&#x8BA4;&#x4F18;&#x5316;&#x7ED3;&#x6784;&#x4F53;&#x7684;&#x987A;&#x5E8F;&#xFF0C;&#x5F53;&#x7136;&#x5E94;&#x8BE5;&#x4E5F;&#x80FD;&#x591F;&#x6307;&#x5B9A;&#x5177;&#x4F53;&#x7684;&#x5185;&#x5B58;&#x5E03;&#x5C40;&#xFF0C;&#x76F8;&#x540C;&#x8BA8;&#x8BBA;&#x8BF7;&#x53C2;&#x8003; <a href="https://github.com/golang/go/issues/10014" target="_blank">Issue10014</a> &#xFF09;&#xFF0C;&#x5185;&#x5B58;&#x4F7F;&#x7528;&#x7387;&#x548C;&#x6027;&#x80FD;&#x90FD;&#x53EF;&#x80FD;&#x4F1A;&#x53D7;&#x76CA;&#x3002;</p>
<p><code>unsafe.Alignof</code> &#x51FD;&#x6570;&#x8FD4;&#x56DE;&#x5BF9;&#x5E94;&#x53C2;&#x6570;&#x7684;&#x7C7B;&#x578B;&#x9700;&#x8981;&#x5BF9;&#x9F50;&#x7684;&#x500D;&#x6570;&#x3002;&#x548C; Sizeof &#x7C7B;&#x4F3C;&#xFF0C; Alignof &#x4E5F;&#x662F;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x5E38;&#x91CF;&#x8868;&#x8FBE;&#x5F0F;&#xFF0C;&#x5BF9;&#x5E94;&#x4E00;&#x4E2A;&#x5E38;&#x91CF;&#x3002;&#x901A;&#x5E38;&#x60C5;&#x51B5;&#x4E0B;&#x5E03;&#x5C14;&#x548C;&#x6570;&#x5B57;&#x7C7B;&#x578B;&#x9700;&#x8981;&#x5BF9;&#x9F50;&#x5230;&#x5B83;&#x4EEC;&#x672C;&#x8EAB;&#x7684;&#x5927;&#x5C0F;&#xFF08;&#x6700;&#x591A;8&#x4E2A;&#x5B57;&#x8282;&#xFF09;&#xFF0C;&#x5176;&#x5B83;&#x7684;&#x7C7B;&#x578B;&#x5BF9;&#x9F50;&#x5230;&#x673A;&#x5668;&#x5B57;&#x5927;&#x5C0F;&#x3002;</p>
<p><code>unsafe.Offsetof</code> &#x51FD;&#x6570;&#x7684;&#x53C2;&#x6570;&#x5FC5;&#x987B;&#x662F;&#x4E00;&#x4E2A;&#x5B57;&#x6BB5; <code>x.f</code>&#xFF0C;&#x7136;&#x540E;&#x8FD4;&#x56DE; <code>f</code> &#x5B57;&#x6BB5;&#x76F8;&#x5BF9;&#x4E8E; <code>x</code> &#x8D77;&#x59CB;&#x5730;&#x5740;&#x7684;&#x504F;&#x79FB;&#x91CF;&#xFF0C;&#x5305;&#x62EC;&#x53EF;&#x80FD;&#x7684;&#x7A7A;&#x6D1E;&#x3002;</p>
<p>&#x56FE; 13.1 &#x663E;&#x793A;&#x4E86;&#x4E00;&#x4E2A;&#x7ED3;&#x6784;&#x4F53;&#x53D8;&#x91CF; x &#x4EE5;&#x53CA;&#x5176;&#x5728;32&#x4F4D;&#x548C;64&#x4F4D;&#x673A;&#x5668;&#x4E0A;&#x7684;&#x5178;&#x578B;&#x7684;&#x5185;&#x5B58;&#x3002;&#x7070;&#x8272;&#x533A;&#x57DF;&#x662F;&#x7A7A;&#x6D1E;&#x3002;</p>
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> x <span class="hljs-keyword">struct</span> {
    a <span class="hljs-keyword">bool</span>
    b <span class="hljs-keyword">int16</span>
    c []<span class="hljs-keyword">int</span>
}
</code></pre>
<p>&#x4E0B;&#x9762;&#x663E;&#x793A;&#x4E86;&#x5BF9;x&#x548C;&#x5B83;&#x7684;&#x4E09;&#x4E2A;&#x5B57;&#x6BB5;&#x8C03;&#x7528;unsafe&#x5305;&#x76F8;&#x5173;&#x51FD;&#x6570;&#x7684;&#x8BA1;&#x7B97;&#x7ED3;&#x679C;&#xFF1A;</p>
<p><img src="../images/ch13-01.png" alt=""></p>
<p>32&#x4F4D;&#x7CFB;&#x7EDF;&#xFF1A;</p>
<pre><code>Sizeof(x)   = 16  Alignof(x)   = 4
Sizeof(x.a) = 1   Alignof(x.a) = 1 Offsetof(x.a) = 0
Sizeof(x.b) = 2   Alignof(x.b) = 2 Offsetof(x.b) = 2
Sizeof(x.c) = 12  Alignof(x.c) = 4 Offsetof(x.c) = 4
</code></pre><p>64&#x4F4D;&#x7CFB;&#x7EDF;&#xFF1A;</p>
<pre><code>Sizeof(x)   = 32  Alignof(x)   = 8
Sizeof(x.a) = 1   Alignof(x.a) = 1 Offsetof(x.a) = 0
Sizeof(x.b) = 2   Alignof(x.b) = 2 Offsetof(x.b) = 2
Sizeof(x.c) = 24  Alignof(x.c) = 8 Offsetof(x.c) = 8
</code></pre><p>&#x867D;&#x7136;&#x8FD9;&#x51E0;&#x4E2A;&#x51FD;&#x6570;&#x5728;&#x4E0D;&#x5B89;&#x5168;&#x7684;unsafe&#x5305;&#xFF0C;&#x4F46;&#x662F;&#x8FD9;&#x51E0;&#x4E2A;&#x51FD;&#x6570;&#x8C03;&#x7528;&#x5E76;&#x4E0D;&#x662F;&#x771F;&#x7684;&#x4E0D;&#x5B89;&#x5168;&#xFF0C;&#x7279;&#x522B;&#x5728;&#x9700;&#x8981;&#x4F18;&#x5316;&#x5185;&#x5B58;&#x7A7A;&#x95F4;&#x65F6;&#x5B83;&#x4EEC;&#x8FD4;&#x56DE;&#x7684;&#x7ED3;&#x679C;&#x5BF9;&#x4E8E;&#x7406;&#x89E3;&#x539F;&#x751F;&#x7684;&#x5185;&#x5B58;&#x5E03;&#x5C40;&#x5F88;&#x6709;&#x5E2E;&#x52A9;&#x3002;</p>

                                
                                </section>
                            
                        </div>
                    </div>
                
            </div>

            
                
                <a href="ch13.html" class="navigation navigation-prev " aria-label="Previous page: 底层编程">
                    <i class="fa fa-angle-left"></i>
                </a>
                
                
                <a href="ch13-02.html" class="navigation navigation-next " aria-label="Next page: unsafe.Pointer">
                    <i class="fa fa-angle-right"></i>
                </a>
                
            
        
    </div>

    <script>
        var gitbook = gitbook || [];
        gitbook.push(function() {
            gitbook.page.hasChanged({"page":{"title":"unsafe.Sizeof, Alignof 和 Offsetof","level":"1.14.1","depth":2,"next":{"title":"unsafe.Pointer","level":"1.14.2","depth":2,"path":"ch13/ch13-02.md","ref":"ch13/ch13-02.md","articles":[]},"previous":{"title":"底层编程","level":"1.14","depth":1,"path":"ch13/ch13.md","ref":"ch13/ch13.md","articles":[{"title":"unsafe.Sizeof, Alignof 和 Offsetof","level":"1.14.1","depth":2,"path":"ch13/ch13-01.md","ref":"ch13/ch13-01.md","articles":[]},{"title":"unsafe.Pointer","level":"1.14.2","depth":2,"path":"ch13/ch13-02.md","ref":"ch13/ch13-02.md","articles":[]},{"title":"示例: 深度相等判断","level":"1.14.3","depth":2,"path":"ch13/ch13-03.md","ref":"ch13/ch13-03.md","articles":[]},{"title":"通过cgo调用C代码","level":"1.14.4","depth":2,"path":"ch13/ch13-04.md","ref":"ch13/ch13-04.md","articles":[]},{"title":"几点忠告","level":"1.14.5","depth":2,"path":"ch13/ch13-05.md","ref":"ch13/ch13-05.md","articles":[]}]},"dir":"ltr"},"config":{"plugins":["katex","-search","-lunr"],"styles":{"website":"styles/website.css","pdf":"styles/pdf.css","epub":"styles/epub.css","mobi":"styles/mobi.css","ebook":"styles/ebook.css","print":"styles/print.css"},"pluginsConfig":{"katex":{},"highlight":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2},"theme-default":{"styles":{"website":"styles/website.css","pdf":"styles/pdf.css","epub":"styles/epub.css","mobi":"styles/mobi.css","ebook":"styles/ebook.css","print":"styles/print.css"},"showLevel":false}},"theme":"default","pdf":{"pageNumbers":true,"fontSize":12,"fontFamily":"Arial","paperSize":"a4","chapterMark":"pagebreak","pageBreaksBefore":"/","margin":{"right":62,"left":62,"top":56,"bottom":56}},"structure":{"langs":"LANGS.md","readme":"preface.md","glossary":"GLOSSARY.md","summary":"SUMMARY.md"},"variables":{},"title":"Go语言圣经","language":"zh-hans","gitbook":"3.x","description":"<The Go Programming Language>中文版"},"file":{"path":"ch13/ch13-01.md","mtime":"2020-08-13T07:15:34.329Z","type":"markdown"},"gitbook":{"version":"3.2.3","time":"2020-08-13T07:17:23.922Z"},"basePath":"..","book":{"language":""}});
        });
    </script>
</div>

        
    <script src="../gitbook/gitbook.js"></script>
    <script src="../gitbook/theme.js"></script>
    
        
        <script src="../gitbook/gitbook-plugin-sharing/buttons.js"></script>
        
    
        
        <script src="../gitbook/gitbook-plugin-fontsettings/fontsettings.js"></script>
        
    

    </body>
</html>

